1. Field of the Invention
The present invention pertains to cementing oil and gas wells with drilling fluid converted to a cementitious slurry which has been treated with a dispersant, is pumped into the space to be cemented sufficiently to displace substantially all of the drilling fluid and which may use one or more basic cement mediums and other additives.
2. Background
In the completion of oil and gas wells, it has been proposed to convert the drilling fluid or "mud" used during well drilling to a cement slurry for cementing casing or tubing in place or otherwise stabilizing or sealing the formation in the vicinity of the borehole. U.S. Pat. Nos. 3,168,139 to H. T. Kennedy, et al; 3,499,491 to R. E. Wyant et al; 3,557,876 to A. Tregasser; 3,887,009 to G. L. Miller et al; and 4,176,720 to William N. Wilson disclose well cement compositions which have been formed at least in part by well drilling fluids.
Many prior art efforts to convert drilling fluid to cement materials have posed certain problems in causing increased viscosity and flocculation of the drilling fluid as the cementitious material is added thereto and pumped into the wellbore. Converted drilling fluid compositions generally along the lines suggested in U.S. Pat. No. 3,499,491, for example, exhibit some gellation and are particularly temperature sensitive. In other words, if wellbore temperatures exceed a predetermined level, the cement composition has a tendency to set or harden rapidly. Since wellbore temperature conditions are difficult to control or predict in many instances, a reduced temperature sensitivity of the drilling fluid converted to cement is highly desirable.
Moreover, with prior art methods and compositions, the displacement of the drilling fluid has been incomplete due to gellation and has often resulted in poor cement bonds or incomplete filling of the casing-to-wellbore annulus with a homogeneous cement. In this regard, the present invention has been developed with a view to providing improved cement compositions through conversion of drilling fluids as well as an improved process for displacing drilling fluid from the wellbore and the casing-to-wellbore annulus so that a complete filling of the space to be cemented is accomplished with a homogeneous cement slurry.